Asbestos is a silicate mineral having a cylindrical form, an acicular (needle-shaped) crystal form, and a fibrous crystal form, excavated from the natural world. There are six kinds of asbestos, which are divided into two mineral groups, that is, a serpentine group and an amphibole group. In particular, tremolite which is one kind of amphibole is formed in a crystal structure having a double chain configured by covalently bonding two or three edges of SiO4 tetrahedrons, as a main frame, as shown in FIG. 1. Here, in the double chain, six SiO4 tetrahedrons are formed in an annular shape, and are repeated, such that the chain is arranged to be long along an axis. The arrangement form allows the tremolite to have fibrous morphological variants.
The asbestos is a silicate mineral originally included in a rock and having a fibrous shape. The asbestos may be easily broken down into fine sized fibers to make thread and cloth, and may be physically robust and chemically inert (against acid and alkali), and have high insulation against electricity and heat.
The asbestos feels like a feather or silk, and has flame retardancy, and is incorrodible, such that it was widely used in more than 3000 various applications such as home appliances, building insulation, automotive brake linings and various industrial processes in the past. However, it became known in the mid-20th century that asbestos causes diseases such as a lung cancer, etc., when inhaled into the respiratory organs, such that various regulations have been implemented. However, since the asbestos have already been used for various materials for a long period of time, the asbestos is widely dispersed in our living environment along with other minerals, such that it is significantly difficult to reduce the concentration thereof.
However, all of the asbestos minerals are not dangerous, but it is dangerous only when the asbestos forms a fibrous shape as shown in FIG. 2A and FIG. 2B. For reference, FIG. 2A is a microscope image of a fiber tissue of Tremolite ([Ca2Mg2SiO8O22(OH)2]n) which is one kind of asbestos, and FIG. 2B is a microscope image of a fiber tissue of Chrysotile ([Mg3Si2O5(OH)4]n) which is also one kind of asbestos.
Once asbestos dust is inhaled through the respiratory organs, it causes health problems. However, it is known that the inhalation of the asbestos dust does not necessarily mean the cause of diseases, but when the asbestos dust of which a length is 5 μm or more, a diameter is 2 μm or less, and an aspect ratio is 5:1 or more is mainly attached to lung tissue, diseases occur. As an inhalation amount of the asbestos dust is increased, and an inhalation period thereof is increased depending on occupations, risk of developing diseases such as asbestosis, lung cancer, mesothelioma, pleural thickening, etc., is also rapidly increased.
Toxicity to a human body caused by the asbestos is related with the kinds of asbestos minerals, a particle size, chemical composition, surface characteristics, durability, etc., of the asbestos mineral. Chrysotile is a type of asbestos that dissolves in a body fluid contained in a lung and has a low toxicity, while tremolite is a type of asbestos that has low solubility and large durability but has the highest toxicity. It is reported from results of a clinical trial that the tremolite excavated in Korea is significantly and highly toxic.
The asbestos is classified as a carcinogenic hazardous material, such that usages thereof are limited. However, the asbestos was widely used for buildings and house wares etc., in the past, such that it is a big challenge to treat waste products thereof, and various technologies for treating waste materials mixed with the asbestos have been developed. A process of removing toxicity to a human body caused by the asbestos refers to “detoxification”, wherein the toxicity to the human body caused by the asbestos is removed mainly by destroying fibrous tissues of the asbestos.
There are technologies of injecting carbon dioxide (CO2) into the asbestos to detoxify the asbestos according to the related art [Japanese Patent Publication No. 4923179 (Feb. 17, 2012), Korean Patent Publication No. 1255849 (Apr. 17, 2013)], wherein the asbestos is pre-treated with a chemical material such as an alkaline solution to separate Ca or Mg from the asbestos such as Tremolite or Chrysotile, and Ca or Mg is combined with the injected CO2, thereby producing carbonate mineral. Through these methods, the fiber tissue which is connected to be long as a chain is destroyed, and a material having the carbonate mineral as a main component is rather produced, such that toxicity to the human body caused by the asbestos may be reduced.
However, the above-described method of asbestos detoxification according to the related art requires the chemical pre-treatment of the asbestos, such that treatment cost may be increased, and another concern for environmental contamination may be included. Further, the chemical treatment of the asbestos allows the asbestos to be converted into the carbonate mineral which is completely different from the asbestos, such that excellent properties of the asbestos are completely lost. Therefore, the above-described method of asbestos detoxification is merely a method of treating waste products mixed with the asbestos, that is, recycling of the asbestos is not considered at all in this technology.